The boring of hard-to-cut materials is generally conducted by an electrochemical machining method or an electric discharge machining method. Particularly, when the boring is conducted on the hard-to-cut materials having a high aspect ratio, it is preferable to use the electrochemical machining method.
Incidentally, for example, a cooling hole for circulating a coolant is provided in a turbine blade of a gas turbine to cool the turbine blade. To increase a cooling efficiency based on the cooling hole, the shape of the cooling hole is preferably curved along a geometric shape of the turbine blade. However, the conventional electrochemical machining method for the turbine blade is suitable to form a straight hole, but it is hard to form a machining hole having a curved shape, i.e. a curved hole.
In Patent Literature 1, a curved hole machining apparatus devised to machine a curved hole is disclosed. In the curved hole machining apparatus, a surface of an electrode tool for machining is partly removed and covered with an insulating member, and thereby a difference in a machined amount is given at a circumferential position of the electrode tool for machining. That is, current density generated between the workpiece and the electrode tool for machining is increased at a portion that is not covered with the insulating member, and thereby an electric field is unevenly distributed at the electrode tool for machining. Therefore, the machined amount is increased at the portion at which the current density is increased, and the electrode tool for machining travels to a side at which the machined amount is great. Thereby, the curved hole is formed.